The invention relates to a synchronous rotary cross-cutter of the type having two oppositely rotated, axially parallel cutting rotors that support cooperating, helically extending knife blades with cutting edges situated in a cylindrical envelope. The axes of these cutting edges run at an angle, corresponding to the inclination of the helix, with respect to the direction of advancement of the material web being cut.
A synchronous cross cutter of this kind is disclosed, for example, in the German Pat. No. 814,236. This device makes it possible to achieve a clean, shearing cut without having to accept a large cutter overlap at the beginning of the knife, which is structurally undesirable in the case of a relatively large material web width. On the other hand, adaption to different cutting lengths is possible with this device only by means of a relatively complex, controllable irregular drive, such as the on described, for example, in the German Pat. No. 933,010.
Synchronous rotary cross cutters with straight knives, which have a knife overlap that increases with the cut width, are thus limited in regard to the width of material web to be cut. On the other hand, it is known from German Pat. No. 2,244,747 to vary the radius of the knives with respect to each particular cutting rotor axis together with the distance of the cutting rotor axes from the material web to accommodate different cutting lengths.